Russell,
I think this is a Windows level problem, I see it in other applications besides VFP. It's like the button sees the downclick but not the upclick event. I think it happens most often when the mouse position is changing during the left button press.
>For quite awhile now, VFP has had an issue with sometimes not closing forms when you click the Close (X) button in the upper right corner of a form. I saw this in VFP 6, 7, and 8. What will happen is that you will click the button, but the form will not close. Then if you drag the mouse pointer back over the close button *without* clicking it, the button will depress and when you drag it off the button it will return to normal.